Remember, she is their teacher as well. She has probably been wanting an excuse to instill some “old school discipline” into them (especially her father Loki ), for quite some time. That is why she was checking her arsenal, for something with suitable heft and power to properly tan their respective hides. And then Thor completely steals her thunder (so to speak), and leaves her dumbstruck.

They must have run throught the course so fast that the judges did not have a chance to evaluate them. And given that lethality was one of the things that the teams were being judged on, that means that each team was probably given a different starting point and route.